1. Field of the Invention
The present invention relates to a lens exchange mount having electrical contacts for transmitting data.
2. Description of the Prior Art
Two automatic exposure control systems are available for automatic exposure control type cameras. The first automatic exposure control system is a shutter-priority system wherein an exposure time or a shutter speed is manually selected by the photographer with priority, and the size of the aperture opening is determined by the camera from the shutter speed thus selected so as to automatically provide suitable exposure. The second automatic exposure control system is an aperture-priority system wherein the aperture size is selected by the photographer, and the exposure time is automatically controlled by the camera so that, again, suitable exposure is provided using the exposure time thus selected.
For convenience in description, the first system will be referred to as "auto", and the second system will be referred to as "manual". The term "manual", as used herein, is broadly defined to also include the case where the photographer manually sets both the shutter speed and the aperture size without using the automatic exposure control of the camera.
In general, in carrying out an automatic exposure control and in displaying the shutter speed and the aperture size according to the automatic exposure, data from the lens, such as the maximum aperture size and the minimum aperture size of the lens, must be transmitted to the camera body when the exchangeable lens is coupled to the camera body. In order to satisfy this requirement, electrial contacts are provided on the confronting surfaces of the mounts of the camera body and of the photographing lens, respectively, so that data from the lens are transmitted, as electrical signals, directly to the camera body from the lens.
FIG. 1 shows a prior art device having electrical contacts for transmitting the "auto" and "manual" switching data. On the camera body, as shown in FIG. 1, an electrical contact 1 is so designed that it does not protrude from a mount surface while, on the photographing lens, an electrical contact 2 is urged to protrude from the mount surface. A switching plate 5 is rocked through a switching member 4 by the "auto" and "manual" switching operation of an aperture control ring 3 so as to cause the urged electrical contact 2 on the photographing lens to retract into and protrude out of the mount surface. Therefore, the electrical contact 2 is moved into and out of engagement with the electrical contact 1 on the camera body so that proper connection and disconnection of the necessary circuits are achieved.
FIG. 2 shows another device having electrical contacts for transmitting the inherent aperture size data of the lens to the camera. As shown in FIG. 2, a switching member 7, provided for fixing ring 6 on the lens, is externally operated to cause an electrical contact 8, integral with the switching member 7, to retract into and protrude out of the lens mount surface so that electrical contact 8 is moved into and out of engagement with an electrical contact 9 on the camera. Thus, proper connection and disconnection of the necessary circuits again are achieved.
However, since a transmitting means, such as the switching member, must be provided or each lens in the above-described prior art devices, the manufacturing cost of the lens barrel is increased. Furthermore, the provision of such a switching member in the lens barrel increases the weight of the lens barrel, and, since there often is little available excess space in the lens barrel, it is thus difficult to design the lens barrel and the lens so that the switching member can be incorporated.